Non-utility owned distributed energy resources (DERs) are mostly untapped currently, but they can provide many grid services such as voltage regulation and service restoration, if properly controlled, and can improve the distribution system's reliability when coordinated with utility-owned assets such as self-healing control and microgrids. This paper integrates transactive energy control into the distribution system reliability evaluation to quantitatively assess the impact of non-utility owned DERs on reliability improvement. A transactive reactive power control strategy is designed to incentivize the DERs to provide reactive power support for improving voltage profiles thus enabling additional customer load restoration during an outage. Also, an operational sequence to coordinate the non-utility owned DERs with the utility owned self-healing control and utility owned microgrids is designed and integrated into the service restoration process with the operational constraints guaranteed by checking the three-phase unbalanced power flow for post-fault network reconfiguration. The reliability indices are then calculated through a Monte Carlo simulation. The transactive reactive power control strategy is tested on a four-feeder distribution system operated by Duke Energy in the U.S. Results demonstrate that the non-utility owned DERs with the transactive control improve the reliability of both the system and critical loads by more than 30%.

Novel power system control and new utility devices need to be tested before their actual deployment to the power grid. To assist with such a testing need, real-time digital emulators such as RTDS and Opal-RT can be used to connect to the physical world and form a hardware in the loop (HIL) emulation. However, due to the limitations of today’s computational resources, the accuracy and fidelity suffer from different levels of model reductions in purely digital simulations. CURENT has developed a reconfigurable electric grid hardware testbed (HTB) to overcome the limitations of digital emulators. The HTB has been used to develop measurement, control, modeling, and actuation techniques for a national grid with a high penetration of renewables. The power electronic-based system includes emulators for synchronous generators; photovoltaics with gridinterfacing inverter; wind turbines; induction motor loads, ZIP loads, power electronic loads; batteries; ac and dc transmission lines; short circuit faults and grid relay protection; and a multiterminal HVDC overlay including power electronics interfaces. The system contains real elements of power flow, measurement, communication, protection, and control that mimic what would be seen in an actual electric grid. This paper presents an overview of the HTB and several scenarios that have been run to determine control and actions needed for the future power grid.

Conventional single-phase H-bridge applications have second-order harmonic ripple power on the dc bus. The second-order harmonic power is usually filtered by a bulk capacitor on the dc bus to maintain a constant dc-bus voltage, which results in low power density. However, in applications like VAr generator, a larger dc-bus voltage fluctuation is acceptable since the dc bus connects to no load. This paper releases the constraints on dc-bus voltage fluctuation so that the dc-bus capacitor can be fully utilized. Based on this idea, an H-bridge-based single-phase VAr generator with minimum dc capacitance is proposed, which reduces the dc-bus capacitor to 1/10th of the size compared to that of the sinusoidal pulse width modulation (SPWM)-modulated H-bridge inverter, without increasing components' count. A general modulation method of the proposed VAr generator is derived to utilize the fluctuating dc-bus voltage. The system volume and power loss are assessed to compare with the conventional SPWM-modulated H-bridge and the circuits with power-decoupling cells. A proportional-integral controller is applied to the system to control the input ac current. The analysis and design are validated by simulations and experiments.

H-bridge based single-phase applications have second-order harmonics on the dc-link voltage. Conventionally, the second-order harmonics are filtered by bulky dc capacitors to maintain the constant dc-link voltage, which results in poor power density and low reliability. However, in applications such as the solid-state variable capacitor (SSVC), the constant dc-link voltage is unnecessary since the dc link is disconnected from load or source. This paper proposes a dc capacitor-less SSVC, which removes the dc capacitors from the topology. The dc voltage is supported by ac side voltage directly. Only a 0.03-p.u. capacitor is needed to filter the switching-frequency harmonics. This enables the proposed SSVC to use the snubber capacitors to achieve the function of the 0.03-p.u. filtering capacitor. Other capacitors can be removed from the dc link busbar. The modulation, modeling, and control strategy of the proposed dc capacitor-less SSVC are provided in this paper. The proposed dc capacitor-less SSVC is validated by the experiment.